Are Engines the Future of Solar Power?

The sun provides the heat but where will they get the 'cold' from to make the engine work?
Del

2000 deg F on hot side, 100 deg F on cold. Should be a reasonably good delta T.

A constant 62°F from a geo-thermal core should be sufficient.

Ever since I've been on CR4 the Stirling Engine has come up time and time again as the solution. They are nearly mythical to me by now. I've never seen, or touched one.

There are some nice ones around, mostly as a kit for under US$100. There is even one that runs when you sit it on a hot cup of Coffee or Tea for under $40 if I remember correctly....

Look here:-

http://www.stirlingengine.com/

There are other kits made of paper cardboard and thin metal sheet that you press out with your fingers and then press together without tools if I remember correctly!!!

Look around on the web.....

Please go to APIX and add that link to the list Garthh put up.

He has decided to revive that particular thread blog as part of the Sustainable Engineering stuff.

We're finally going to stop kicking the can and light a fire under it eh?

Well a fire under it will at least get the A***hole" sitting on top to move away damn quick!

I happen to be working on an engine for solar power as well. I think there are several issues that should be addressed with renewable energy to become viable as a part of the base load of an electricity grid.

- Energy should be supplied around the clock (24/24h)

- Production should be able to follow demand

- Cost should be competitive with current fossil fuel (or perhaps slightly higher if accepted by client)

- Production should not have negative side effects (like water usage in dry sunny areas)

- Production should be at reasonable distance from consumers

- Required surface on earth should be available

This means that energy storage becomes key to success of renewables.

There are various ways of storing energy. Chemical (in batteries), Potential (hydrodams), pressurized air in underground reservoirs, heat (molten salts for example), cold (phase change materials, for example locally in places where air conditioners are being used).

Hydrodams are commonly used worldwide but their potential in dry sunny areas is limited because of lack of water. Other technologies are being evaluated at present.

Batteries are quite expensive.

Pressurized air is imho not mature since nothing is being done yet with the heat that results from pressurizing. But this can become an interesting option.

Heat storage is already used in several concentrated solar power (CSP) plants and it works fine at reasonable cost. The plants can operate around the clock.

CSP has the advantage that supplements of energy can be obtained by burning fossil fuel or biofuel when the sky is cloudy for longer periods of time. The same installations are used but they are complemented with burners. The storage of fossil/bio fuel is furthermore cheap.

Comes the issue of water usage: current CSP plants use steam turbines in which the Rankine cycle requires heat rejection (in the condenser). Traditional wet cooling (concrete cooling towers) costs about 3.7 cubic meters of water per MWh. That is why CSP plants in dry Arizona and Nevada are converting to capital intensive dry cooling (1 million euro instead of 300.000 Euro per MW). There are alternatives however. For example use open cycle gas turbines instead of closed cycle steam turbines as is currently done in Israël. At heat2power we work on open cycle piston engine for CSP that also does not need cooling in the thermodynamic cycle. This option also potentially offers higher efficiencies than turbines for power less that 10 MW. And the engines can be scaled from 3kW up to 10MW. Because the heat2power engines are based on conventional engine layout the production cost per kW should be low compared to turbines.

The above makes us believe that CSP with engines can become part of the base load of electricity grids easier than photovoltaics or wind power.

- Cost should be competitive with current fossil fuel (or perhaps slightly higher if accepted by client)

Fossil fuel costs are artificially inflated due big oil having us over a barrel; no pun intended, economic feasibility will allow the fossil fuel cost to be significantly reduced especially in light of the surplus of OPEC production and the idiocy in the reason for shutting down refineries. We could see fuel at $35USD/barrel, can you compete in that scenario?

If you structured the field in a manner to compete at $31USD/barrel for five years your energy production concept would enable large investment in infrastructure.

I think we can only dream about 35$ a barrel. Oil companies have understood they make astronomical profits with scarcity in the market. And then there is Peak Oil that may have an influence on price. I estimate the chances to drop to 35$ are quite low. Please visit www.peakoil.nl and download newsletter on http://www.peakoil.nl/wp-content/uploads/2009/11/2009_November_Oilwatch_Monthly.pdf and more generally applied on other materials : http://www.materialscarcity.nl/systems/file_download.aspx?pg=162&ver=1

Changed the title to reflect the content better.

Hi Andy, Good to see you on this topic.

Sorry to bother you with this but our engine is NOT a Stirling engine. Would you then change the title (again) to "heat engines" to cover other engines as well.

BTW I can recommend a book : the evolution of the heat engine , by Ivo Kolin. ISBN 0-9652455-2-7. It contains a rich collection of engines that run on external heat sources.

As for the Stirling engine I find that the power density in W per € (including maintenance) is too low to be really performant for solar power. But that is a personal opinion. At the moment Infinia (www.infiniacorp.com) is selling Stirling solar dishes at 15000 USD per 3kW and they have an order book of 2 billion USD. Mainly military... to save fuel at the front that costs between 70-100 USD per gallon in total. The market is still very young and I expect a lot to change with time.

Happy new year to all of you on this thread.

Your wish is my command Sir!